ILOVAYSK, Ukraine — Russian-backed separatists moved some heavy weapons well back from the front line Tuesday in eastern Ukraine, but the Ukrainian government disputed the rebels' claim that a real pullback had begun.

A peace plan worked out in marathon talks on Feb. 12 aims to create a wide buffer zone between the two sides' artillery, part of efforts to end the conflict that has left nearly 5,800 dead since April. Heavy weapons are to be pulled back 25 to 70 kilometers (15 to 45 miles) from the front line, depending on their caliber.

The disagreement over a weapons pullback came as the fragile peace deal for Ukraine was discussed in Paris by the foreign ministers of Russia, Ukraine, Germany and France. The talks ended without apparent progress, although the participants pledged adherence to the peace deal.

Ukrainian Foreign Minister Pavlo Klimkin told reporters that rebel shelling of Ukrainian positions had to stop before Ukraine started withdrawing its artillery. "You can't pull out ... while shelling is coming down on you," he said.

Russia denies Ukrainian and Western claims that it is supplying the rebels with troops and equipment, but Western officials and NATO insist that satellite photos show Russian military equipment in eastern Ukraine.

Eduard Basurin, a top rebel commander in the Donetsk region, said his side had begun a large-scale pullback of heavy weapons in line with the peace plan, but the claim could not be verified. A rebel website quoted him as saying about 100 122-mm howitzers would be involved.

Associated Press reporters saw about a dozen howitzers moved from Donetsk, the largest rebel-held city, to the town of Ilovaysk 20 kilometers (12 miles) to the east. That would put them roughly within the 25-kilometer (15-mile) pullback criterion for weapons of that size.

Michael Bociurkiw, a spokesman for the international team monitoring the fighting, said he couldn't confirm any pullback until receiving monitors' reports, possibly at the end of the day.

The Ukrainian military dismissed the rebel pullback claim and said its forces would not withdraw their weapons until a cease-fire takes hold. Ukrainian military spokesman Col. Andriy Lysenko said no Ukrainian moves to withdraw were underway.

The rebels "are just regrouping their gangs and are relocating their weapons," he told reporters. "As soon as there is a cease-fire for two days, that is the signal to start a withdrawal."

AP journalists on Tuesday saw Ukrainian self-propelled artillery units and tanks moving toward the government-held town of Artemivsk, away from the area around the key rail hub of Debaltseve. Ukrainian forces abandoned Debaltseve last week after a weeks-long rebel siege.

British Prime Minister David Cameron on Tuesday said a resurgence of fighting to that level could bring new Western restrictions on Russia.

"If there is another Debaltseve it will trigger a round of sanctions that will be materially different to what we have seen before," Cameron told a parliamentary committee.

In Washington, Secretary of State John Kerry said Russia has been "persisting in their misrepresentations, lies, whatever you want to call them."

The supposed cease-fire in eastern Ukraine has been tested by violations. On Tuesday, military spokesman Lt. Col. Anatoliy Stelmakh said the rebels had shelled the town of Popasna seven times and launched one barrage on the village of Luhanske.

Stelmakh also said rebels tried to storm Ukrainian positions near the southern village of Shyrokyne, which is near the strategic Azov Sea port of Mariupol.

Concerns persists that the rebels aim to take Mariupol to help establish a land corridor between mainland Russia and the Crimean Peninsula, which Russia annexed last March.

Klimkin said Ukraine was concerned about a possible relocation of rebel forces from Debaltseve to the Mariupol area and warned that any further rebel attack would mean the peace effort was abandoned, and prompt a "decisive counterattack."